Support for grAb chunk in PNG images, and propagation of values when converting PNGs to patches (which won't be necessary pretty soon).

git-svn-id: http://mancubus.net/svn/hosted/eternity/trunk@2729 86ba831e-150c-0410-ab35-e06eaae15ed9
Pass correct address to png_set_read_user_chunk_fn O_O

git-svn-id: http://mancubus.net/svn/hosted/eternity/trunk@2730 86ba831e-150c-0410-ab35-e06eaae15ed9